sets and bolts crown block to posts at top of derrick. Strings cables through pulleys and blocks. Clamps holding fixture on end of hoisting cable. Weighs clay, and mixes drilling mud, using portable power mixer. Starts pumps that circulate mud through drill pipe and borehole to cool drill bit and flush out drill-cuttings. Cleans and oils pulleys, blocks, and cables. May repair pumps pump servicer. [-] Less